1. Field of the Invention
This invention relates to the field of foam-forming equipment for fire extinguishing purposes, and more particularly to nozzles for the application of a foam formed from a liquid and foam-stabilizer mix.
2. Description of the Prior Art
Fire-fighting nozzles for the application of a water stream or a water fog have been known for some time. Such nozzles are attached to a fire hose and are adjusted to apply the fire-extinguishing liquid in a pattern ranging from a fog-like application to a straight stream. Liquid mixtures containing a foam-stabilizing concentrate have also been utilized in fire-fighting nozzles for the extinguishing of certain types or classes of fires. These foam-stabilizing concentrates will, when mixed with a liquid, aerated, and mechanically agitated, form a relatively stable foam that is particularly useful for the extinguishing of large fires.
The stabilizer is generally supplied as a concentrate that is inducted into the flowing liquid stream to form mixture. Examples of such liquid foam-stabilizing concentrates are known under the trademarks, Light Water.RTM. "AFFF," Light Water.RTM. "AFFF/ATC" of Minnesota Mining and Manufacturing Company, Minnesota and "Emulsiflame.TM." of Elkhart Brass Manufacturing Co., Inc. Other such stabilizers are generally described in U.S. Pat. Nos. 3,772,195; 3,562,156; 3,578,590; and 3,548,949.
The inventions described in U.S. Pat. Nos. 4,497,442 and 4,640,461 disclose nozzles for applying a foam wherein a foam-stabilizing concentrate is inducted into a segment of a general flowing liquid stream, such as water, through the nozzle. In these inventions, the general inner bore of the nozzle communicates a liquid stream from a hose to the point of discharge. Educator means within the inner bore extracts a foam-stabilizing concentrate from a supply and inducts it into a previously separated first segment of the liquid stream flowing through the general inner bore. At the discharge stem end of the nozzle the concentrate and liquid is agitated and aerated in a foam-forming chamber to form a stabilized foam and mixed with the remainder of the liquid stream. After combination with the remainder of the liquid stream, the foam is "thrown" in a desired pattern. An adjustable flow regulating means can regulate the rate of flow (gallons per minute) of the stream discharged.
The nozzle of U.S. Pat. No. 4,497,442 improved the focus for the foam-liquid mixture discharged from the nozzle, reducing the dispersion of the foam stream from that discharged by previous nozzles. As a result, the nozzle of U.S. Pat. No. 4,497,442 could apply or throw the foam over a greater distance than previous foam nozzles, without the utilization of subsidiary pump means, thereby allowing the fire-fighter to operate a simplified nozzle and be freely removed from the fire.
A general limitation, however, affecting the above inventions, and other nozzles, is that the nozzles are unable to produce, within the expansion range applicable to fire-fighting nozzles, a relatively highly aerated foam, with homogeneous bubbles, and also quickly adjust to supply a less-aerated foam with a higher, more optimal throw. Ideally, the fire-fighter should be able to quickly and easily adjust between an optimal foam and an optimal throw as conditions dictate. Highly aerated foam is advantageous in that it is more effective on polar solvent and alcohol fires. An optimal throw permits the fire-fighter to remain further removed from the fire and is suitable for hydrocarbon fires. The amount of agitation required to produce an optimal expansion varies with the concentrate formulation, water temperature, and water purity.